Number of vertices in all ordered (plane) trees with n edges that are at distance two from all the leaves above them.

A121320

Number of vertices in all ordered (plane) trees with n edges that are at distance two from all the leaves above them.

Terms

    a(0) =0a(1) =0a(2) =1a(3) =2a(4) =6a(5) =18a(6) =59a(7) =203a(8) =724a(9) =2643a(10) =9802a(11) =36755a(12) =138935a(13) =528406a(14) =2019419a(15) =7748125a(16) =29825844a(17) =115132729a(18) =445498768a(19) =1727434607a(20) =6710501025a(21) =26110567532a(22) =101744332967a(23) =396983837719

External references